The value of virtual currency Bitcoin has reached an all-time high, trading at more than $33 (£22). Its appreciation - up from just $2 in November 2011 - has been attributed to increased trust in security efforts. The surge coincided with Japan-based MT Gox, Bitcoin's biggest exchange, announcing a tie-up with US firm CoinLab to bring its operations to the States. However, recent high-profile thefts continue to worry some investors. In September last year, 24,000 Bitcoins - which at the time were worth £157,800 - were stolen from another large exchange, Bitfloor. In June 2011, a huge ... (